In a standard x-y plotter, one or more felt tip or ball point pens, normally of different colors, are mounted in suitable holders in a pen stocker. The plotter is programmed to move a pen carriage to position a holder on the carriage to pick up a selected pen from the stocker and to move the pen carriage and either a slider on which the carriage is mounted or a paper or other medium mounted under the carriage through a predetermined path or paths to cause the pen to draw desired images on the medium. In such devices, the pen will tend to rotate slightly in the holder in use and there may be substantial rotation of the pen as a result of transfers between the stocker holder and the carriage holder. While such rotation of the pen relative to the holder is not a problem when ball point or felt tip pens are utilized, and is in fact desirable to equalize wear, it is a problem when the plotter is utilized to do calligraphy, utilizing a calligraphy-style fountain pen.
When a fountain pen is used in the plotter, point shape and ink flow vary with annular orientation of the pen; therefore, the shape, thickness and intensity of the line being drawn by the pen are dependent on the pen orientation. Therefore, to obtain desired stroke thickness and uniform (or at least controlled) stroke appearance when using a plotter to do calligraphy with a fountain pen, it is necessary that the annular orientation of the pen in the carriage holder be the same each time a pen is picked up by the carriage holder from a stocker holder and that the annular orientation of the pen be maintained in the carriage holder while the pen is in use. In order to accomplish this objective, a desired annular orientation must be maintained for the pen in both the stocker holder and the carriage holder.